1. Field of the Invention
Co-channel signals are the most difficult type of interference signals to remove as they occur on the same frequency as the desired signal and therefore are not amenable to conventional filtering techniques. The seriousness of the co-channel interference problem is heightened due to the fact that it is not restricted to receiving sites located at appreciable distances from two transmitters, but can be at any distance from a transmitting site due to the production of `ghosts` or reflections of the desired signal from nearby obstructions which are in effect co-channel interference signals.
2. Description of the Prior Art
Prior art which is currently employed to reduce the effects of co-channel interference on television reception includes carrier beat note filters and antenna arrays.
Typical carrier beat note filters can attenuate the 10 to 20KHz beat frequency usually found between co-channel carriers, but such filters cannot eliminate the complete interference. For example, superimposed pictures are not eliminated by this technique.
Systems which use an auxiliary antenna directed at the interference signal source and adjust the phase and amplitude of the interference signal to cancel the interference signal received by the main array required skill in adjustment as both phase and amplitude controls must be adjusted simultaneously in order to null the interference. Only one setting for both controls will produce cancellation and this point must be found if any significant cancellation is to occur. The auxiliary antenna must be directed at the interference source requiring the operator to know the source of interference. If more than one independent source of interference exists, then multiple systems and antennas are required to eliminate the interference. These and other problems are overcome by the present invention.